Evolutionarily stable foraging speeds in feeding scrambles: a model and an experimental test

Abstract

An evolutionarily stable strategy (ESS) model of scramble effort (for example, foraging speed) in competition for food or mates, where payoff may depend on competitor density, is described. An individual can increase speed (at some energetic cost) to gain a greater share of resources. The predictions are that if food input per competitor is constant (density independence), the ess foraging speed should increase with density, but if food input per patch is constant (density dependence), then the ESS foraging speed should decrease with density. The predictions of this model are tested in an experiment using different densities of cichlid fish, Aequidens portalegrensis , scrambling for food at a discrete resource patch. The results provide support for the model in a situation where payoffs are density dependent, but fit less well where they are density independent.